Vibrations in Foundations. The Factors which Affect the Natural Frequency of Foundations, and the Ef

In spite of the growing importance of suspension bridges for long spans, English text-books on the theory of structures commonly either make no reference to suspension bridges or else give only a brief account of Rankine's approximate theory.' In the latter case it is usual to outline the method as applied to a bridge with a three-hinged stiffening girder, to mention that the results so obtained overestimate the bending actions on the girder, and perhaps to indicate that, with still less accuracy, the method can be applied to the case of a two-pinned girder. If anything is said of the "deflection theory" in common use in the U.S.A., and outlined in some American text-books2, 3, it is usual only to remark on its greater accuracy without giving much indication of its essential nature and limitations. Professor A.G. Pugsley